1. Field of the Invention
The present invention generally relates to a method of recording eccentricity correction data in a disk-shaped recording medium, a recording medium in which eccentricity correction data are recorded in accordance with the recording method, a method of controlling a head position based on the eccentricity correction data, and an information recording and reproducing apparatus, and more particularly to a method of recording eccentricity correction data in a disk-shaped recording medium in which eccentricity correction can be efficiently controlled, a recording medium in which eccentricity correction data are recorded in accordance with the recording method, a method of controlling a head position by using the eccentricity correction data, and an information recording and reproducing apparatus.
2. Description of the Related Art
For a recording apparatus using a disk-shaped recording medium, such as a hard disk drive apparatus, there is a demand of shortening the track pitch of the disk-shaped recording medium for the purpose of improving the recording density. As the track pitch is shortened, an allowable amount of off-track slice is made smaller, resulting in more significant errors of eccentricity. This eccentricity is caused by so-called “repeatable runout (RRO)” due to decentering of the center axis of the recording medium at servo track write (STW) time before shipment of the disk drive apparatus and at medium loading time into the disk drive apparatus.
In order to make the eccentricity smaller, for example, the following process is performed at an earlier step of an examination process before the shipment. First, in order to detect an amount of eccentricity correction, a digital signal processor (DSP) of a disk drive apparatus is used to perform discrete Fourier transform (DFT) on position data obtained through servo demodulation for a certain cylinder of a medium. The detected eccentricity correction amount is stored in a memory of DSP as an eccentricity correction table. Furthermore, the eccentricity correction table is stored in a flash ROM (Read Only Memory). At time of the next activation, the eccentricity correction table is read from the flash ROM and transferred to the DSP memory. Based on the eccentricity correction table, DSP controls eccentricity correction. As a result, it is possible to make an on-track operation stable throughout all cylinders for each recording and reproducing head.
Such cylinder/track eccentricity of a disk-shaped recording medium includes many order components (frequency components) from various factors. For low-order eccentricity data such as the first-order and the second-order components, even if a seek operation is performed toward a cylinder adjacent to a currently on-tracked cylinder, the phase component of the eccentricity data hardly changes. For high-order eccentricity data greater than or equal to the fourth order, however, if an on-tracked cylinder is shifted into the adjacent cylinder thereof, the phase component of the eccentricity data substantially changes (See FIG. 1 and FIG. 2). In such a case where the phase component of eccentricity changes, there is a risk that the eccentricity cannot be corrected at appropriate timing with respect to control operations. In this case, a current suitable to control the position of a recording and reproducing head cannot be supplied to a voice coil motor (VCM). As a result, the eccentricity correction cannot be properly controlled, thereby increasing RRO. Thus, it may be difficult to make the recording and reproducing head stationary on a certain cylinder.
In order to address the above-mentioned problem, DSP computes a difference between an initial low-order eccentricity in an initial eccentricity correction table and the currently detected corresponding order eccentricity together with a high-order eccentricity correction amount in real-time during an on-track operation (See FIG. 3).
Japanese Laid-Open Patent Applications No. 09-091903, No. 2001-195196, No. 11-232810, No. 2002-352535, No. 08-063916 and No. 09-128915 describe the related art.
In the above-mentioned method, however, the following problem may occur during seek operations to shift the recording and reproducing head from the cylinder, on which the head remains stationary, to another cylinder or immediately after seek operations including head switch operations. Namely, there arises a difference between high-order eccentricity data of a cylinder on-tracked by the recording and reproducing head previously, which are recorded for each recording and reproducing head by DSP, and actual eccentricity of a currently on-tracked cylinder. As a result, since the head positions cannot be controlled stably, there is a risk that a write operation may fail even if a seek operation is completed.
FIG. 1 and FIG. 2 are diagrams illustrating exemplary eccentricity data of cylinders of a disk-shaped recording medium after shipment. As shown in FIG. 1, phase differences between adjacent cylinders are small with respect to the low-order components (the first-order through the third-order components). However, as shown in FIG. 2, phase differences between adjacent cylinders are considerable with respect to high-order components (the 16th-order through the 18th-order components).
FIG. 3 shows an exemplary eccentricity correction step in a sequential read operation executed by a conventional disk drive apparatus.
Referring to FIG. 3, when a seek instruction is provided to DSP of the disk drive apparatus at step S1, DSP executes the seek instruction at step S2. At step S3, DSP reads an initial eccentricity correction table as described above as soon as the seek operation is completed. Then, DSP performs an eccentricity correction control operation based on the initial eccentricity correction table. Here, HDC does not start to read and write data until the eccentricity correction control operation becomes able to stably control head positions (steps S4 and S5).
In order to ensure that the recording and reproducing head can be positioned on an intended cylinder and the recording and reproducing head can be made stationary there, it is necessary to provide an initial eccentricity correction table specific to each cylinder and each recording and reproducing head and then position the recording and reproducing head precisely based on the initial eccentricity correction table.
In accordance with the above-mentioned Japanese Laid-Open Patent Application No. 09-091903, eccentricity correction data are written in servo information recorded in a medium in advance. In the disclosed method, whenever the servo information on the medium is read, an optimal amount of eccentricity correction is determined for a current position, and an eccentricity correction operation is optimally controlled at the current on-track position. However, according to the disclosed method, since the correction control data are written together with the servo information on the medium, it is necessary to provide a hardware device to write the correction control data. In addition, since the eccentricity correction data are written immediately after the servo information, there is a risk that the servo information may be erroneously overwritten due to rotational variations of the medium and an instable stationary status of the writing head during write operations.
Also, it is preferable to prepare eccentricity data with respect to all orders corresponding to the number of heads for each cylinder as initial eccentricity correction amounts so as to position the heads on target tracks stably. From the viewpoint of the size of an available memory, however, it is difficult to store such all-order eccentricity data on a large number of cylinders, for example, more than 10000 cylinders, for each disk drive apparatus into a flash ROM. In one approach to address the problem, a medium is divided, for example, into four areas between the outer circumferential area and the center area. For each area, one cylinder is selected, and initial low-order eccentricity correction amounts (for example, the first-order and the second-order components) are provided. Then, when data are recorded or reproduced in/from the medium, DSP performs a real-time eccentricity correction operation on all cylinders in the above-mentioned fashion.